A polarizing film is normally colored and molded to have a concave and convex surface while it is interposed between a plastic lens or a glass lens, and used as sunglasses. In the course of molding the colored polarizing film, a reference mark is applied onto the polarizing film in a polarizing direction (in a direction of a polarizing axis) for convenient assembly of the sunglasses. Although the application of the reference mark onto the polarizing film is effected manually for every colored polarizing film using a marker having a specific ink, the operation thereof is however complicated.
Meanwhile, JP-A 2002-512379 discloses a vacuum molding method of molding a polarizing lens. The vacuum molding method is adapted for mass production but not adapted for large item small scale production.